A microsporidian, Nosema algerae, originally described as a hyperparasite of anopheline mosquitoes, has been found to parasitize larval stages of Fasciola hepatica during their development in the snail intermediate host. The primary objective of this study is to determine if field applications can be made using this organism against Fasciola-infected snails from regions of Montana where fascioliasis is a livestock disease problem The long-term objectives are: 1.) Snail collections from irrigated areas in the state where livestock production is prevalent. Cultivation and maintenance of field collected snails as well as the laboratory reared young snails, maintaining a controlled environment to ensure growth and development for future experimentation. Preparation of snails for shipment to the National Museum of Natural History for identification. 2.) Experimental infections of laboratory reared snails with miracidia of Fasciola hepatica. The miracidia will be hatched from the ova of flukes recovered from bovine livers obtained from packing plants. This experiment will be used to determine susceptible strains or species of snails. 3.) Experimental exposure of Fasciola hepatica infected snails to Nosema algerae, to determine its' effectiveness as a biological control agent. 4.) Examination of field collected wild snails for the evidence of new species of parasites, pathogenic organisms, or predators.